Darren Bent, as pretty much every article about him over the past couple of days has mentioned, scored 32 goals in 58 Premier League games for Sunderland. That is a lot, and especially at a club without a great recent history of scoring goals in bulk.

He was the first Sunderland player to score for England since Len Shackleton. Last season, it was his upsurge in form with a hat-trick against Bolton Wanderers, combined with Craig Gordon's return from a broken arm and a rare window in John Mensah's injury nightmare, that ensured Sunderland stayed up. Only the most blinkered of revisionists would suggest he was anything other than a very useful player for Sunderland.

Even this season, when his form has been less certain, he has managed eight goals in 20 league games, but what is intriguing is what has happened in the three games he has missed (his durability, incidentally, starting 58 of 61 possible league games in his time at Sunderland, is another asset). In those games, Sunderland beat Stoke City 2-0 at home in a game they controlled and would have won more comfortably but for a penalty miss from Steed Malbranque; they scrapped their way to a slightly fortunate 1-1 draw at Tottenham Hotspur; and they produced the best Sunderland performance in a decade to win 3-0 at Chelsea.

It is those latter two games that are most telling. Sunderland this season have taken 11 points from 11 away games. Last season they took 10 from 19. Repeatedly, they have found themselves overrun through the centre of midfield. It also happened this season in the home game against Everton when Sunderland got away with a 2-2 draw. It happened to an extent against Newcastle United on Sunday. Most crushingly, it happened in the away game at Newcastle that directly preceded that run of three matches Bent missed; then, Sunderland coped with Newcastle for 15 minutes or so, but when Kevin Nolan was withdrawn into a deeper position and, outnumbered, they surrendered the centre, then surrendered everything else and lost 5-1. It would be absurd to say that is Bent's fault, but his style of play has knock-on effects.

Over the past two seasons, in 61 league games, Sunderland varied from 4-4-2 on only 10 occasions. Bent is a willing runner and led the line better than many who would dismiss him as purely a finisher might expect. Away against Tottenham last season, when Sunderland were excellent in losing 2-0 and most of the attention on Bent focused on his penalty miss rather than his all-round display, he looked as though he may be developing an aptitude for the position.

It did not, though, come naturally to him, and he looked far better in partnership with either Kenywne Jones or Fraizer Campbell. He never struck up a similar understanding with Asamoah Gyan. Perhaps that was because creator-finisher or senior-junior roles were never as clearly defined, but it should be borne in mind that there were very few games when both were fully fit and able to play together.

But with a regular goalscorer (bought for £10m) and a £13m striker who had been one of the stars of the World Cup, it was very hard for Steve Bruce to leave either out, something that became very apparent after the Chelsea match. Bent returned from injury and Danny Welbeck, who had probably been Sunderland's best player at Stamford Bridge, linking centrally between Gyan and the midfield, was shoved out to the wing for the 2-2 draw with Everton. Sunderland have never regained the same fluency since.

The options now seem simpler for Bruce. He can play Gyan as a lone striker with Welbeck to one side and another wide player (Steed Malbranque? Jordan Henderson? Ahmed Elmohamady? Kieran Richardson? Campbell, as and when he returns from his knee injury? A new signing bought with some of the £24m raised for Bent?) to the other, which would allow a central midfield three and so provide greater resilience than Sunderland have often shown in those areas over the past two seasons. Or he can play 4-4-2 with Welbeck just off Gyan, as he was at Chelsea.

Given Campbell's injury, Bruce's first priority is a forward to offer cover for Gyan and Welbeck, particularly given it could be six weeks until the latter is back after exploratory surgery on a troublesome knee. Longer term, he needs either to buy or replace Welbeck when his loan spell expires at the end of the season. Attacking width, particularly on the right, is another area Sunderland are short, something Bruce has acknowledged by admitting his interest in PSG's Stéphane Sessègnon.

And if the thinking is of a move to a system with three central midfielders (although Bruce has played 4-4-2 or 4-4-1-1 in 85.1% of his 314 league games as a manager), another central midfielder is probably necessary to fill the role of deep-lying distributor (ideally with bite) vacated by Lorik Cana in the summer. The Paraguay international Cristian Riveros was presumably supposed to be that replacement, but he has started only four league games since his summer move from Cruz Azul. Lee Cattermole, a far better passer than he is often given credit for, fulfils the Cana role to an extent, but his regular suspensions mean there must be back-up – and a ball-winning partner at the back of the midfield might cut down on the number of lunging challenges he feels compelled to make.

Losing Bent, of course, is a wrench, and Sunderland fans who have invested emotional energy in him understandably feel aggrieved. But at least the break was swift, and if the £24m is properly invested, it can only be to the long-term benefit of the club. Some prices are simply too good to turn down, particularly if the player is disaffected, as Bent's recent form suggested he was. There are, after all, few things that smack of a small-club mentality more than desperately clinging to stars who have no desire to be there any more, as though there is no possibility any better player could be daft enough to make the same mistake as they did and sign up to replace them.

There are those who worry about how Sunderland will replace Bent's goals, but goals are a strange thing. Towards the end of Michael Owen's time at Liverpool, his apologists regularly pointed to his goals tally – 70 league goals in his last four seasons. But the question is the cost of those goals. In Liverpool's case, playing to Owen made them predictable; in Sunderland's case it was an open midfield. Having one primary goalscorer tends to mean a side is one-dimensional. Now for a team that had spent most of the last decade with no effective dimensions, that was a huge step in the right direction for Sunderland. One functioning dimension will probably save you from relegation – although while Gérard Houllier clearly thinks Bent will save Aston Villa, he couldn't save Charlton Athletic in 2006-07 – but a side that sees itself as a regular challenger for European football needs more than that.

This feels like a critical point for Sunderland. It might be the moment at which the slowly mounting optimism of the past few months is popped, but it might just be the moment at which they emerge as a modern, two-dimensional team.